U.S. patent application number 11/226493 was filed with the patent office on 2007-03-15 for process for isomerizing non-equilibrium xylene-containing feed streams.
Invention is credited to John E. Bauer, Paula L. Bogdan, Robert B. Larson, Michael H. Quick, James E. Rekoske, Patrick C. Whitchurch.
Application Number | 20070060778 11/226493 |
Document ID | / |
Family ID | 37856198 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070060778 |
Kind Code |
A1 |
Bogdan; Paula L. ; et
al. |
March 15, 2007 |
Process for isomerizing non-equilibrium xylene-containing feed
streams
Abstract
Reduced co-production of toluene and C.sub.9 and higher
aromatics such as trimethylbenzene, methylethylbenzene, and
diethylbenzene is achieved in processes for the isomerization of
xylenes to close to equilibrium using a layered catalyst having a
thin outer layer of molecular sieve and hydrogenation metal
component on a core, wherein at least about 75 mass-% of the
hydrogenation metal component is in the outer layer.
Inventors: |
Bogdan; Paula L.; (Mount
Prospect, IL) ; Rekoske; James E.; (Glenview, IL)
; Larson; Robert B.; (Chicago, IL) ; Whitchurch;
Patrick C.; (Villa Park, IL) ; Bauer; John E.;
(LaGrange Park, IL) ; Quick; Michael H.;
(Arlington Heights, IL) |
Correspondence
Address: |
HONEYWELL INTELLECTUAL PROPERTY INC;PATENT SERVICES
101 COLUMBIA DRIVE
P O BOX 2245 MAIL STOP AB/2B
MORRISTOWN
NJ
07962
US
|
Family ID: |
37856198 |
Appl. No.: |
11/226493 |
Filed: |
September 14, 2005 |
Current U.S.
Class: |
585/481 |
Current CPC
Class: |
C07C 5/2737 20130101;
Y02P 20/52 20151101; C07C 5/2775 20130101; C07C 5/2737 20130101;
C07C 15/08 20130101; C07C 15/08 20130101; C07C 5/2775 20130101 |
Class at
Publication: |
585/481 |
International
Class: |
C07C 5/22 20060101
C07C005/22 |
Claims
1. A process for isomerizing xylene in a feedstock comprising a
non-equilibrium mixture of one or more xylenes comprising
contacting the feedstock with a catalytically-effective amount of
layered catalyst under isomerization conditions sufficient to
provide a xylene-containing isomerization product stream in which
of the xylenes, para-xylene comprises at least about 23 mass-%,
ortho-xylene at least about 21 mass-%, and meta-xylene at least
about 48 mass-%, said catalyst comprising a core having a major
dimension of at least about 300 microns, a layer on said core, said
layer comprising molecular sieve having a pore diameter of from
about 4 to 8 angstroms and a binder and having a thickness less
than about 250 microns, and at least one hydrogenation metal
component selected from metals of Groups 6 to 10 of the Periodic
Table (IUPAC), wherein at least about 75 mass-% of the
hydrogenation metal component in the catalyst is contained in the
layer, wherein the net production of toluene and trimethylbenzene
is less than about 3 mass-% of the total xylenes and ethylbenzene,
if present, in the feedstock.
2. The process of claim 1 wherein the feedstock contains less than
about 5 mass-% para-xylene based on total xylenes and the
isomerization product stream contains at least about 23.5 mass-%
para-xylene based on total xylenes in the product stream.
3. The process of claim 2 wherein the binder comprises aluminum
phosphate.
4. The process of claim 2 wherein the molecular sieve comprises at
least one of MFI, MEL, MTT, UZM-8 and MTW molecular sieves.
5. The process of claim 4 wherein the layer has a thickness between
about 20 and 200 microns.
6. The process of claim 5 wherein the hydrogenation metal component
comprises at least one of molybdenum, rhenium, ruthenium, rhodium,
palladium, iridium, and platinum.
7. The process of claim 1 wherein the core comprises alumina.
8. The process of claim 7 wherein the core comprises
alpha-alumina.
9. The process of claim 1 wherein the core has a spherical
structure.
10. The process of claim 1 wherein the core has a monolithic
structure.
11. The process of claim 1 wherein the feedstock comprises
ethylbenzene.
12. The process of claim 11 wherein the isomerization conditions
include ethylbenzene dealkylation conditions and the feedstock
contains less than 0.5 mass-% naphthenes.
13. The process of claim 12 wherein at least about 50 mass-% of the
ethylbenzene is converted.
14. The process of claim 12 wherein the hydrogenation metal
component comprises molybdenum.
15. The process of claim 12 wherein the binder comprises aluminum
phosphate.
16. The process of claim 12 wherein the hydrogenation metal
component is platinum.
17. The process of claim 11 wherein the feedstock comprises
naphthenes and the isomerization conditions include ethylbenzene
isomerization conditions.
18. The process of claim 1 wherein the feedstock has been subjected
to dealkylation prior to isomerization.
19. The process of claim 18 wherein the net production of
naphthenes is less than about 0.02 mass-% of the total xylenes and
ethylbenzene in the feedstock.
20. The process of claim 18 wherein the hydrogenation metal
component comprises rhenium.
Description
FIELD OF THE INVENTION
[0001] This invention relates to catalytic processes for the
isomerization of xylenes with desirably low C.sub.8 aromatic ring
loss as observed by co-production of toluene and
trimethylbenzene.
BACKGROUND OF THE INVENTION
[0002] Numerous processes have been proposed for the isomerization
of one or more of xylenes (meta-xylene, ortho-xylene and
para-xylene) to form other isomers of xylene. In many instances,
the sought xylene isomer is para-xylene due to the demand for
terephthalic acid for the manufacture of polyester.
[0003] In general, these xylene isomerization processes comprise
contacting the xylene isomer sought to be isomerized with an
isomerization catalyst under isomerization conditions. Various
catalysts have been proposed for xylene isomerization. These
catalysts include molecular sieves, especially molecular sieves
contained in a refractory, inorganic oxide matrix. The catalysts
also contain a hydrogenation metal, such as a platinum group
metal.
[0004] Due to the large scale of commercial facilities to produce
para-xylene on an economically competitive basis, not only must a
xylene isomerization process be active and stable, but it also must
not unduly convert xylenes to other aromatics or crack the aromatic
feed so as to result in ring loss. Toluene and trimethylbenzene are
two of the typical co-products from an isomerization and, because a
loss in C.sub.8 aromatic values results from such co-production,
processes to reduce their co-production are sought. Typically, the
loss in C.sub.8 aromatic values increases as the isomerization
process is driven closer to equilibrium. Accordingly, to minimize
the loss of C.sub.8 aromatic values, commercial facilities often
suffer inefficiencies by not driving the isomerization close to
equilibrium.
[0005] Catalytic processes are sought that reduce the loss of
C.sub.8 aromatic values and thus reduce the co-production of
toluene and trimethylbenzene and other C.sub.9 and higher aromatics
while allowing closer approaches to xylene isomerization
equilibrium to be achieved.
[0006] U.S. Pat. No. 4,362,653, for instance, discloses a
hydrocarbon conversion catalyst which could be used in the
isomerization of isomerizable alkylaromatics that comprises
silicalite (having an MFI-type structure) and a silica polymorph.
The catalyst may contain optional ingredients. Molybdenum is listed
as one of the many optional ingredients. U.S. Pat. No. 4,899,012
discloses catalyst for isomerization and conversion of ethylbenzene
containing a Group VIII metal, lead, a pentasil zeolite and an
inorganic oxide binder. U.S. Pat. No. 6,573,418 discloses a
pressure swing adsorption process to separate para-xylene and
ethylbenzene from C.sub.8 aromatics. Included among the catalysts
disclosed for ethylbenzene isomerization are those containing ZSM-5
type of molecular sieve (Al-MFI) dispersed on silica. The catalysts
contain a hydrogenation metal and listed among the hydrogenation
metals are molybdenum. Suitable matrix materials are said to be
alumina and silica. See example 12 which uses a
molybdenum-containing catalyst for xylene isomerization. U.S. Pat.
No. 6,143,941 discloses selective isomerization and ethylbenzene
conversion processes using catalysts comprising a zeolite,
including MFI-type zeolites, a platinum group metal and an
aluminophosphate binder.
[0007] U.S. Pat. No. 4,899,011 discloses a two catalyst system for
xylene isomerization and ethylbenzene dealkylation in which the
first catalyst, which has low ethylbenzene diffusivity, dealkylates
ethylbenzene, and the second catalyst, which has a greater
ethylbenzene diffusivity, effects xylene isomerization.
[0008] U.S. Pat. No. 6,280,608 discloses layered catalysts
containing a core and an outer layer containing molecular sieve and
catalytic metals. One of the potential uses for the layered
catalyst is said to be for isomerization reactions.
SUMMARY OF THE INVENTION
[0009] In accordance with this invention processes for the
isomerization of xylenes are provided that exhibit reduced C.sub.8
ring loss by the co-production of toluene and C.sub.9 and higher
aromatics such as trimethylbenzene, methylethylbenzene, and
diethylbenzene while achieving a xylene isomerization close to
equilibrium. These processes use a catalyst having a core, or
support, upon which a thin layer of molecular sieve and
hydrogenation metal component is placed. This thin layer uses a
binder preferably containing aluminum phosphate. The catalysts used
in the processes of this invention have at least about 75,
preferably at least about 90, mass-% of the hydrogenation metal in
the thin layer. Not only do the composite catalysts used in this
invention provide the sought reduced co-production of toluene and
C.sub.9 and higher aromatics even at close approaches to xylene
equilibrium, but also, if desired, the amount of molecular sieve
and hydrogenation metal per unit volume of reactor can be reduced.
Moreover, the composite catalyst can have shapes such as rings,
saddles, and honeycombs, which shapes are not as readily achievable
with a homogeneous catalyst composition.
[0010] The broad aspects of the processes of this invention for
isomerizing xylene in a feed stream comprising a non-equilibrium
mixture of one or more xylenes comprise contacting the feed stream
with a catalytically-effective amount of layered catalyst under
isomerization conditions sufficient to provide a xylene-containing
isomerization product stream in which of the xylenes, para-xylene
comprises at least about 23 mass-%, ortho-xylene at least about 21
mass-%, and meta-xylene at least about 48 mass-%, said catalyst
comprising a shape-defining core, preferably having a major
dimension of at least about 300 microns, a layer on said core. The
core is shape-defining, i.e., the core, and not the layer, defines
the geometric configuration of the catalyst. The layer is typically
the outer layer of the catalyst; however, it is within the scope of
this invention that an additional layer may be placed on the
catalyst that does not adversely affect the catalytic performance
of the layer. For sake of ease of reference herein, the layer will
be referred to herein as the outer layer.
[0011] The outer layer comprises molecular sieve having a pore
diameter of from about 4 to 8 angstroms, at least one hydrogenation
metal component and a binder. The outer layer has a thickness less
than about 250, preferably between about 20 and 200, and more
preferably between about 20 and 150, microns. The at least one
hydrogenation metal component is selected from metals of Groups 6
to 10 of the Periodic Table (IUPAC), wherein at least about 75
mass-% of the hydrogenation metal component in the catalyst is
contained in the layer. In the processes of this invention, the net
production of toluene and trimethylbenzene is less than about 3,
preferably less than about 2.5, and most preferably less than about
2, mass-% of the total xylenes and ethylbenzene, if present, in the
feed stream.
[0012] Preferably, the processes are used in the production of
para-xylene and the feed stream contains less than about 5 mass-%
para-xylene based on total xylenes. Under conditions where
ethylbenzene is dealkylated or the feed contains little or no
ethylbenzene, the approach to equilibrium can often be such that
the isomerization product contains at least about 23.5, and more
preferably at least about 23.7, mass-% para-xylene based on total
xylenes.
[0013] In a further preferred aspect of the processes of the
invention, the feed stream contains ethylbenzene, e.g., from about
1 to 60 mass-% based upon total C.sub.8 aromatics, and the
ethylbenzene is dealkylated.
[0014] In a further preferred aspect of the processes of this
invention wherein the feed stream comprises ethylbenzene and a
non-equilibrium mixture of xylenes, the ethylbenzene is either
isomerized or dealkylated. The isomerization or dealkylation may be
effected using the layered catalyst. In an alternate aspect of the
processes of this invention, the feed stream is contacted with a
catalyst suitable for ethylbenzene dealkylation under ethylbenzene
dealkylation conditions to provide a dealkylation product stream
which is then contacted with the layered catalyst for effecting
isomerization of xylenes. Preferably, for ethylbenzene
dealkylation, the feed stream contains less than about 0.5 mass-%
naphthenes.
DETAILED DISCUSSION
CATALYST
[0015] The processes of this invention use a layered catalyst
composition. The layered catalyst composition comprises an inner
core and an outer layer containing molecular sieve and
hydrogenation metal component. The composite catalyst may be of any
suitable structure and configuration and made by any suitable
process. For instance, see U.S. Pat. No. 6,280,608 and U.S. Pat.
No. 6,710,003 disclose layered catalyst compositions and their
preparation and are hereby incorporated in their entireties by
reference.
[0016] The core may be of any suitable material capable of
providing the structure and tolerating the process conditions. The
core may be homogeneous or may itself be a composite. The preferred
composition of the core is one that does not have significant
adverse effect in the isomerization process. Thus, the core would
have a substantially lower catalytic activity for isomerization
relative to the outer layer. The inner core may be essentially
inert in the process environment. The characteristics of the inner
core should also be properly matched with those of the outer layer,
such that a strong, attrition resistant bond is formed during the
composition preparation steps outlined hereinafter.
[0017] Examples of the inner core materials include, but are not
limited to, refractory inorganic oxides, silicon carbide, and
metals. Examples of refractory inorganic oxides include without
limitation cordierite, alpha alumina, theta alumina, magnesia,
zirconia, titania and mixtures thereof. A preferred inorganic oxide
is alpha alumina. Other core materials include clays such as
montmorillonite, saponite, kaolinite, and bentonite. The core may
be composed of metals and ceramic-coated metals. Advantageously,
the material of the core and that of the layer have similar
coefficients of expansion over the temperature ranges to which the
composites are exposed during preparation and use.
[0018] The materials that form the inner core can be formed into a
variety of shapes such as pellets, extrudates, spheres, rings,
trilobes, saddles, or other physical forms including monoliths such
as honeycomb structures, plates, tubes, and the like. Of course,
not all materials can be formed into each shape. The core typically
has a major dimension, usually at least about 300 microns, which is
in excess of the thickness of the outer layer and thus
significantly defines the shape of the composite catalyst.
[0019] One broad grouping of preparation techniques to make the
inner core include oil dropping, pressure molding, metal forming,
pelletizing, granulation, extrusion, rolling methods and
marumerizing. A spherical inner core is commonly used, although
pressure drop considerations can warrant the use of shaped articles
that result in a higher void fraction when such shapes are packed
into a catalyst bed. The inner core whether spherical or not has an
effective diameter of about 0.05 mm to about 5 mm and preferably
from about 0.4 mm to about 3 mm. For a non-spherical inner core,
effective diameter is defined as the diameter the shaped article
would have if it were molded into a sphere. Once the inner core is
prepared, it is calcined at a temperature of about 400.degree. to
about 1500.degree. C.
[0020] The outer layer contains molecular sieve and binder.
Molecular sieves include those having Si:AI.sub.2 ratios greater
than about 10, and often greater than about 20, such as the MFI,
MEL, EUO, FER, MFS, MTT, MTW, TON, MOR, UZM-8 and FAU types of
zeolites. Pentasil zeolites such as MFI, MEL, MTW and TON are
preferred, and MFI-type zeolites, such as ZSM-5, silicalite,
Borolite C, TS-1, TSZ, ZSM-12, SSZ-25, PSH-3, and ITQ-1 are
especially preferred where ethylbenzene is dealkylated. MTW-type
molecular sieves are especially preferred for processes in which
ethylbenzene is isomerized.
[0021] The relative proportion of molecular sieve in the outer
layer may range from about 1 to about 99 mass-%, with about 2 to
about 90 mass-% being preferred. A refractory binder or matrix is
typically used to facilitate fabrication of the isomerization
catalyst, provide strength and reduce fabrication costs.
[0022] The binder should be uniform in composition and relatively
refractory to the conditions used in the process. Suitable binders
include inorganic oxides such as one or more of alumina, aluminum
phosphate, magnesia, zirconia, chromia, titania, boria and silica.
The catalyst also may contain, without so limiting the composite,
one or more of (1) other inorganic oxides including, but not
limited to, beryllia, germania, vanadia, tin oxide, zinc oxide,
iron oxide and cobalt oxide; (2) non-zeolitic molecular sieves,
such as the aluminophosphates of U.S. Pat. No. 4,310,440, the
silicoaluminophosphates of U.S. Pat. No. 4,440,871 and ELAPSOs of
U.S. Pat. No. 4,793,984; and (3) spinels such as MgAI.sub.2O.sub.4,
FeAI.sub.2O.sub.4, ZnAI.sub.2O.sub.4, CaAI.sub.2O.sub.4, and other
like compounds having the formula MO--Al.sub.2O.sub.3 where M is a
metal having a valence of 2; which components can be added to the
composite at any suitable point.
[0023] A preferred binder or matrix component, especially for
processes also involving the dealkylation of ethylbenzene,
comprises an amorphous phosphorous-containing alumina (hereinafter
referred to as aluminum phosphate) component. The atomic ratios of
aluminum to phosphorus in the aluminum phosphate binder/matrix
generally range from about 1:10 to 100:1, and more typically from
about 1:5 to 20:1. Preferably, the aluminum phosphate has a surface
area of up to about 450 m.sup.2/g, and preferably the surface area
is up to about 250 m.sup.2/g. See, for instance, U.S. Pat. No.
6,143,941.
[0024] The thickness of the outer layer is less than about 250
microns and preferably is less than 200 microns, for instance, 20
to 200, microns. Often the thickness is within the range of about
20 to 100 microns. Preferably, the thickness is such that a
combination of adequate catalytic activity for the isomerization
with low activity for transalkylation, which transalkylation
results in C.sub.8 ring loss, is achieved. Without wishing to be
limited to theory, it is believe that the close approaches to
xylene isomerization equilibrium with little co-production of
toluene and C.sub.9 and higher aromatics of the processes of this
invention are, in part, enabled by the use of a thin outer layer
that facilitates diffusion of the aromatics to and from
catalytically active sites, and the presence of catalytically
active sites for the isomerization located close to the surface of
the catalyst composite. Accordingly, the outer layer should be
sufficiently thin that the net production of toluene and
trimethylbenzene is less than about 3, preferably less than about
2.5, and most preferably less than about 2, mass-% of the total
xylenes and ethylbenzene (if present) in the feed stream. And by
having the catalytically active sites for the isomerization
clustered in this thin, outer layer, the sought catalytic
isomerization activity for xylene isomerization can be
achieved.
[0025] The outer layer can be applied to the core in any suitable
manner. If desired, a bonding layer may be used to assist in
adhering the outer layer to the core. In many instances, the
coating can be directly applied to the core. The outer layer
comprises molecular sieve and binder. It is often possible to
synthesize molecular sieve, e.g., MFI, in situ as a layer on the
core by various techniques. See, for instance, U.S. Pat. No.
6,090,289 and references cited therein for techniques to make
molecular sieve films on supports. In such processes, the binder
may be coated on the core prior to or after the in situ synthesis
of the molecular sieve.
[0026] Alternatively, the molecular sieve and the binder slurry may
be preformed and coated on the core. The binder may be in the form
of a sol, hydrosol or acidic sol, or the like. The amount of the
sol contained in the slurry is based upon the desired ratio of
binder to molecular sieve. If desired, the slurry may contain one
or more bonding agents to aid in adhesion to the core and improve
the strength of the outer layer. Examples of bonding agents include
but are not limited to polyvinyl alcohol (PVA), hydroxy propyl
cellulose, methyl cellulose, and carboxy methyl cellulose. The
amount of organic bonding agent which is added to the slurry will
vary considerably from about 0.1 to about 5 mass-% of the slurry.
Depending on the particle size of the outer layer, it may be
necessary to mill the slurry in order to reduce the particle size
and simultaneously give a narrower particle size distribution. This
can be done by means known in the art such as ball milling for
times of about 30 minutes to about 5 hours and preferably from
about 1.5 to about 3 hours. Often the slurry for coating the core
has a sufficient liquid (usually water) content that the viscosity
is in the range from about 30 to 600 centipoise (millipascal
second) at 25.degree. C.
[0027] Coating of the inner core with the slurry can be
accomplished by means such as rolling, dipping, spraying, etc. to
yield a coated core having an outer layer. One coating technique
involves using a fixed fluidized bed of inner core particles and
spraying the slurry into the bed to coat the particles evenly. The
thickness of the layer of the coated core can vary considerably,
but usually is from about 5 to about 250 microns, preferably from
about 10 to about 200 microns, with the average coating thickness
being between about 20 and 200 microns.
[0028] Once the inner core is coated with the outer bound zeolite
layer, the resultant coated core is dried at a temperature of about
50.degree. to about 300.degree. C. for a time of about 1 to about
24 hours to provide a dried coated core. Subsequently, the dried
coated core is calcined at a temperature of about 400.degree. to
about 900.degree. C. for a time of about 0.5 to about 10 hours to
effectively bond the outer layer to the inner core and provide the
layered catalyst composition of the present invention. The
calcination step also removes any remaining organic template
material within the molecular sieve as well as any residual bonding
agent. In some cases, the catalyst may be activated in a modified
calcination step wherein the organic template is first decomposed
in a flow of pure nitrogen. The oxygen concentration is then
gradually increased to combust any residual hydrocarbons in the
zeolite. It is also possible to combine the drying and calcining
operations into a single step. If desired, the calcination can
occur subsequent to impregnation of hydrogenation metal
component.
[0029] If desired, the composite structure, before or after
impregnation with the hydrogenation metal component, can be
subjected to steaming to tailor its acid activity. The steaming may
be effected at any stage, but usually is carried out on the
composite prior to incorporation of the hydrogenation metal
component. Steaming conditions comprise a water concentration of
about 5 to 100 vol-%, pressure of from about 100 kPa to 2 MPa, and
temperature of between about 600.degree. and 1200.degree. C.; the
steaming temperature preferably between about 650.degree. and
1000.degree. C., more preferably at least about 750.degree. C. and
optionally may be about 775.degree. C. or higher. In some cases,
temperatures of about 800.degree. to 850.degree. C. or more may be
employed. The steaming should be carried out for a period of at
least one hour, and periods of 6 to 48 hours are preferred.
[0030] Alternatively or in addition to the steaming, the composite
may be washed with one or more of a solution of ammonium nitrate, a
mineral acid, and/or water. Considering the first alternative, the
catalyst may be washed with a solution of about 5 to 30 mass-%
ammonium nitrate. When acid washing is employed, a mineral acid
such as HCI or HNO.sub.3 is preferred; sufficient acid is added to
maintain a pH of from more than 1 to about 6, preferably from about
1.5 to 4. The catalyst is maintained in a bed over which the
solution and/or water is circulated for a period of from about 0.5
to 48 hours, and preferably from about 1 to 24 hours. The washing
may be effected at any stage of the preparation, and two or more
stages of washing may be employed.
[0031] Prior to addition of the hydrogenation metal component the
composite preferably is ion-exchanged with a salt solution
containing at least one hydrogen-forming cation such as
NH.sub.4.sup.+ or quaternary ammonium. The hydrogen-forming cation
replaces principally alkali-metal cations to provide, after
calcination, the hydrogen form of the zeolite component.
[0032] One or more hydrogenation metal components are provided.
Hydrogenation metal components are selected from the metals of
Groups 6 to 10 of the Periodic Table (IUPAC), preferably
molybdenum, rhenium and platinum-group metal. Preferred
platinum-group metals include one or more of platinum, palladium,
rhodium, ruthenium, osmium, and iridium. The most preferred
platinum-group metals are platinum and palladium, with platinum
being especially preferred.
[0033] The hydrogenation metal component is contained in the outer
layer of the catalyst composite. The location of the hydrogenation
metal component within the catalyst can often be determined by
scanning electron microscopy. At least about 75, and preferably at
least about 90, mass-% of the hydrogenation metal component is
within the outer layer. As the outer layer contains the molecular
sieve, a close association of molecular sieve to the hydrogenation
metal is assured. While not wishing to be limited by theory, the
close association of the hydrogenation metal with the molecular
sieve is believed to aid in reducing transalkylation reactions
leading to the generation of toluene and C.sub.9 and higher
aromatics.
[0034] Any suitable technique may be used to selectively provide
the hydrogenation metal component in the outer layer. For instance,
the hydrogenation metal component may not be attracted by the
material of the core, the hydrogenation metal component may be
composited with the material of the outer layer prior to making the
layered catalyst composite, the binder may be selected such that
the hydrogenation metal component is deposited therein as opposed
to the material of the core, the surface of the core may be
relatively impermeable to the hydrogenation metal component or
precursor, or the hydrogenation metal component deposition
technique may be such that the component becomes fixed in the outer
layer prior to being able to pass to the core.
[0035] With respect to platinum group metals, the platinum-group
metal component may exist within the final catalyst composite as a
compound such as an oxide, sulfide, halide, oxysulfide, etc., or as
an elemental metal or in combination with one or more other
ingredients of the catalyst composite. It is believed that the best
results are obtained when substantially all of the platinum-group
metal component exists in a reduced state. The platinum-group metal
component generally comprises from about 10 to about 10,000
mass-ppm (parts per million) of the outer layer of the composite,
calculated on an elemental basis, with a level of about 100 to
about 2000 mass-ppm being particularly suitable. When using a
platinum component, very low levels of about 100 to 500 mass-ppm of
platinum based on the outer layer of the catalyst, on an elemental
basis, are favored. When using a palladium component, levels of
about 200 to 2000 mass-ppm of palladium based on the outer layer,
on an elemental basis, are favored.
[0036] The platinum-group metal component may be incorporated into
the catalyst composite in any suitable manner. One method of
preparing the catalyst involves the utilization of a water-soluble,
decomposable compound of a platinum-group metal to impregnate the
outer layer. Alternatively, a platinum-group metal compound may be
added at the time of compositing the outer layer. Yet another
method of effecting a suitable metal distribution is by compositing
the metal component with the binder prior to applying the coating
to make the outer layer. Complexes of platinum-group metals which
may be employed according to the above or other known methods
include chloroplatinic acid, chloropalladic acid, ammonium
chloroplatinate, bromoplatinic acid, platinum trichloride, platinum
tetrachloride hydrate, platinum dichlorocarbonyl dichloride,
tetraamineplatinum chloride, dinitrodiaminoplatinum, sodium
tetranitroplatinate (II), palladium chloride, palladium nitrate,
palladium sulfate, diaminepalladium (II) hydroxide,
tetraaminepalladium (II) chloride, and the like.
[0037] Where the hydrogenation metal comprises molybdenum,
molybdenum is usually present in an amount of 0.1 to 5 mass-% based
upon the mass of the outer layer. One useful process for making the
catalysts comprises forming the catalyst composite without the
molybdenum component and then impregnating or otherwise depositing
on the composite with a molybdenum compound such as ammonium
heptamolybdate, molybdenum trioxide, ammonium dimolybdate,
molybdenum oxychloride, molybdenum halides, e.g., molybdenum
chloride and molybdenum bromide, molybdenum carbonyl,
phosphomolybdates, and heteromolybdic acids. Usually water soluble
molybdenum compounds are selected as the source of the molybdenum
component for the catalyst. The molybdenum-containing catalysts may
also contain at least one platinum group metal as a hydrogenation
metal catalyst components. Usually, the molybdenum (calculated on
an elemental basis) comprises at least about 60 atomic-percent,
preferably at least about 80 atomic-percent to essentially all, of
the hydrogenation metal (elemental basis) of the hydrogenation
component. Often, the platinum group metal present is in an amount
of 20 to 500 mass-ppm based on the mass of the outer layer.
[0038] After addition of the hydrogenation metal component, the
resultant catalytic composite usually is dried at a temperature of
about 100.degree. to about 320.degree. C. for a period of from
about 1 to about 24 or more hours. The dried composite then is
calcined at a temperature of from about 400.degree. to about
600.degree. C. in an air atmosphere for a period of from about 0.1
to 10 hours to convert the metallic components substantially to the
oxide form.
[0039] The calcined composite optimally is subjected to a
substantially water-free reduction step to ensure a uniform and
finely divided dispersion of the optional metallic components. The
reduction optionally may be effected on the catalyst as loaded in
the isomerization-process reactor of the present invention prior to
the startup of the isomerization process. Substantially pure and
dry hydrogen (i.e., less than 20 vol-ppm H.sub.2O) preferably is
used as the reducing agent in this step. The reducing agent
contacts the catalyst at conditions, including a temperature of
from about 200.degree. to about 650.degree. C. and for a period of
is from about 0.5 to about 10 hours, effective to reduce
substantially all of the platinum group metal component to the
metallic state. The catalysts of the may contain a halogen
component, comprising fluorine, chlorine, bromine or iodine or
mixtures thereof, with chlorine being preferred. Preferably,
however, the catalyst contains no added halogen other than that
associated with other catalyst components. In some cases the
resulting reduced catalyst composite may also be beneficially
subjected to presulfiding by a method known in the art to
incorporate in the catalyst composite from about 0.01 to about 0.5
mass-% sulfur, calculated on an elemental basis, into the
catalyst.
[0040] With respect to hydrogenation components from Groups 6 and
7, especially molybdenum-containing catalysts and
rhenium-containing catalysts, the hydrogenation metal component
generally comprises from about 0.1 to about 5 mass-% of the final
catalyst calculated as hydrogenation component being the elemental
metal based upon the mass of the outer layer. The hydrogenation
metal component may exist within the final catalyst composite as a
compound such as an oxide, sulfide, halide, oxysulfide, etc., or as
an elemental metal or in combination with one or more other
ingredients of the catalyst composite.
[0041] The hydrogenation metal component may be incorporated into
the catalyst composite in any suitable manner. One method of
preparing the catalyst involves the utilization of a water-soluble,
decomposable compound of the hydrogenation metal to impregnate the
calcined sieve/binder composite. Alternatively, a hydrogenation
metal compound may be added at the time of compositing the sieve
component and binder.
[0042] The catalyst composites are dried at a temperature of from
about 100.degree. to about 320.degree. C. for a period of from
about 2 to about 24 or more hours. If desired, the catalyst may be
calcined at a temperature of from about 400.degree. to about
650.degree. C. in an air atmosphere for a period of from about 0.1
to about 10 hours. Steam may also be present during the
calcination, e.g., from about 0.5 to 20, say, about 1 to 10, mol-%
steam based on the air.
[0043] In some cases, the catalyst composite may also be
beneficially subjected to presulfiding by a method known in the art
to incorporate in the catalyst composite from about 0.05 to about
1.0 mass-% sulfur calculated on an elemental basis. Particularly
advantageous catalysts are sulfided sufficiently to enhance
activity, and this sulfiding may be through presulfiding, or adding
a sulfur-containing sulfiding agent to the feedstream during use of
the catalyst. Preferably, the elemental ratio of sulfur to
molybdenum is between about 0.01:1 to 3:1, more preferably, about
0.1 to 2:1.
[0044] If desired, the catalyst may contain, as a minor portion of
the hydrogenation catalyst component, a platinum-group metal,
including one or more of platinum, palladium, rhodium, ruthenium
osmium, and iridium. In any event, the Group 6 or 7 hydrogenation
metal component comprises at least about 60 atomic-percent,
preferably at least about 80 atomic-percent to essentially all, of
the hydrogenation metal (elemental basis) of the hydrogenation
component. Often, any platinum group metal present is in an amount
of 20 to 500 mass-ppm based on the outer layer. Where the catalyst
contains a minor amount, based on total hydrogenation metal, of
platinum group metal, the resultant calcined composites often are
subjected to a substantially water-free reduction step to ensure a
uniform and finely divided dispersion of the optional metallic
components. The reducing agent contacts the catalyst at conditions,
including a temperature of from about 200.degree. to about
650.degree. C. and for a period of from about 0.5 to about 10
hours, effective to reduce substantially all of the platinum group
metal component to the metallic state. It is within the scope of
the present invention that the catalyst may contain other metal
components known to modify the effect of the hydrogenation metal
component. Such metal modifiers may include without so limiting the
invention rhenium, tin, germanium, lead, cobalt, nickel, indium,
gallium, zinc, and mixtures thereof. Catalytically effective
amounts of such metal modifiers may be incorporated into the
catalyst by any means known in the art to effect a homogeneous or
stratified distribution.
[0045] Where a molybdenum-containing catalyst is used, sometimes
sulfiding can enhance isomerization activity. Sulfiding conditions
are those in which the sulfiding agent is incorporated into the
catalyst without forming sulfur dioxide. The sulfiding may be done
during the catalyst preparation or thereafter, including as a
pretreatment at catalyst start-up or during use of the catalyst.
The sulfiding may be conducted in any convenient manner. For
instance, a solid or sorbed sulfur-containing component, i.e.,
sulfiding agent, may be incorporated into the catalyst composite
which decomposes during the catalyst preparation or during start-up
or use of the catalyst. Alternatively, the formed catalyst may be
contacted with a liquid or gaseous sulfiding agent under sulfiding
conditions. Examples of sulfiding agents include hydrogen sulfide,
carbonyl sulfide, carbon disulfide, salts, especially ammonium and
organo salts, of sulfates, bisulfates, sulfites, and bisulfites,
sulfur dioxide, sulfur trioxide, organosulfides, e.g., dimethyl
sulfide, diethyl sulfide, and methyl ethyl sulfide; mercaptans,
e.g., methyl mercaptan, ethyl mercaptan, and t-butyl mercaptan;
thiophenes, e.g., tetrahydrothiophene.
[0046] The sulfiding conditions can vary widely and will depend
upon the nature to the sulfiding agent and the extent of sulfiding
desired. For instance, with oxygen-containing sulfur compounds, the
sulfiding conditions should be sufficient to reduce the sulfur
moiety to sulfide. The selection of the sulfiding conditions will
also be influenced limits of feasibility at the location of the
catalyst undergoing sulfiding. Thus, different conditions may be
preferred where the sulfiding is being conducted after the catalyst
has been installed in a reactor for the isomerization as would be
preferred where the catalyst is at a facility for the manufacture
of catalyst. In general, the sulfiding may be conducted over a
temperature range of 0.degree. to 600.degree. C., preferably about
10.degree. to 500.degree. C. and a pressure of from about 10 to
5000 or more kPa absolute. The duration of the sulfiding will
depend upon the other conditions of the sulfiding, e.g., the
sulfiding agent, the concentration of the sulfiding agent, and
sulfiding temperature, as well as the amount of sulfur to be
incorporated into the catalyst. Usually the sulfiding is conducted
for a period of time of at least about 10 minutes, and may, in the
case of in situ sulfiding in an isomerization reactor, be
continuous. Where the sulfiding is accomplished during the
preparation of the catalyst, the sulfiding is usually done over a
period of at least about 10 minutes, e.g., 10 minutes to 24 hours.
Often, the sulfiding is done in the presence of hydrogen, e.g., at
a partial pressure of about 10 to 5 MPa.
[0047] Where sulfiding is done while the catalyst is in an
isomerization reactor, the sulfiding may be accomplished as a
pretreatment or during the isomerization process itself. In the
latter case, the sulfiding agent is usually provided in a low
concentration, e.g., less than about 50, say about 0.001 to 20,
mass-ppm of the feedstock.
[0048] Catalysts may be regenerated. Where the loss of catalytic
activity is due to coking of the catalyst, conventional
regeneration processes such as high temperature oxidation of the
carbonaceous material on the catalyst may be employed.
PROCESS
[0049] The feedstocks to the aromatics isomerization process of
this invention comprise non-equilibrium xylene and ethylbenzene.
These aromatic compounds are in a non-equilibrium mixture, i.e., at
least one C.sub.8 aromatic isomer is present in a concentration
that differs substantially from the equilibrium concentration at
isomerization conditions. Thus, a non-equilibrium xylene
composition exists where one or two of the xylene isomers are in
less than equilibrium proportion with respect to the other xylene
isomer or isomers. The xylene in less than equilibrium proportion
may be any of the para-, meta- and ortho-isomers. As the demand for
para- and ortho-xylenes is greater than that for meta-xylene,
usually, the feedstocks will contain meta-xylene. Generally, the
mixture will have an ethylbenzene content of about 1 to about 60
mass-%, an ortho-xylene content of 0 to about 35 mass-%, a
meta-xylene content of about 20 to about 95 mass-% and a
para-xylene content of 0 to about 30 mass-%. Usually the
non-equilibrium mixture is prepared by removal of para-, ortho-
and/or meta-xylene from a fresh C.sub.8 aromatic mixture obtained
from an aromatics-production process. The feedstocks may contain
other components, including, but not limited to naphthenes and
acyclic paraffins, as well as higher and lower molecular weight
aromatics.
[0050] The alkylaromatic hydrocarbons may be used in the present
invention as found in appropriate fractions from various refinery
petroleum streams, e.g., as individual components or as certain
boiling-range fractions obtained by the selective fractionation and
distillation of catalytically cracked or reformed hydrocarbons.
Concentration of the isomerizable aromatic hydrocarbons is
optional; the process of the present invention allows the
isomerization of alkylaromatic-containing streams such as catalytic
reformate with or without subsequent aromatics extraction to
produce specified xylene isomers and particularly to produce
para-xylene. In some instances, the feedstocks contain less than
about 0.5, more preferably less than about 0.1, mass-%
naphthenes.
[0051] Often the feedstocks will contain ethylbenzene, and in such
instances, the ethylbenzene content is typically about 1 to about
60 mass-% of the total feedstock. In an aspect of this invention,
an ethylbenzene containing feedstock is first subjected to
catalytic dealkylation conditions to reduce the ethylbenzene
content, and then subjected to the isomerization using the layered
catalysts.
[0052] In the processes of this invention in which ethylbenzene is
isomerized, typically the feed also contains naphthenes in an
amount sufficient to enhance the ethylbenzene conversion.
Naphthenes are cyclic paraffins and may include, for purposes
herein, cyclic compounds having non-aromatic unsaturation in the
ring structure. A convenient source of naphthenes is the
isomerization process itself which produces naphthenes. Typically,
the naphthenes that are recycled are monocyclic compounds,
especially 5 and 6 carbon atom rings, having from 5 to 9 carbon
atoms. The downstream unit operations will define the composition
and amount of naphthenes being recycled. Generally, the naphthenes
are present in an amount of about 2 to 20, preferably from about 4
to 15, mass-% of the feed. Equilibria may exist under isomerization
conditions between naphthenes and aromatics. Thus, at isomerization
conditions that convert a greater percentage of ethylbenzene,
greater concentrations of naphthenes are preferred. As the
naphthenes are a by-product of the isomerization, usually the
isomerization unit is started up with the xylene and ethylbenzene
feed and then the sought amount of naphthenes are permitted to
build up for steady-state operation.
[0053] According to the process of the present invention, the
feedstock, in the presence of hydrogen, is contacted with the
layered catalyst described above. Contacting may be effected using
the catalyst system in a fixed-bed system, a moving-bed system, a
fluidized-bed system, and an ebullated-bed system or in a
batch-type operation. In view of the danger of attrition loss of
valuable catalysts and of the simpler operation, it is preferred to
use a fixed-bed system. In this system, the feed mixture is
preheated by suitable heating means to the desired reaction
temperature, such as by heat exchange with another stream if
necessary, and then passed into an isomerization zone containing
catalyst. The isomerization zone may be one or more separate
reactors with suitable means therebetween to ensure that the
desired isomerization temperature is maintained at the entrance to
each zone. The reactants may be contacted with the catalyst bed in
upward-, downward-, or radial-flow fashion.
[0054] The isomerization is conducted under isomerization
conditions including isomerization temperatures generally within
the range of about 100.degree. to about 550.degree. C. or more, and
preferably in the range from about 150.degree. to 500.degree. C.
The pressure generally is from about 10 kPa to about 5 MPa
absolute, preferably from about 100 kPa to about 3 MPa absolute.
The isomerization conditions comprise the presence of hydrogen in a
hydrogen to hydrocarbon mole ratio of between about 0.5:1 to 6:1,
preferably about 1.1 or 2:1 to 5:1. A sufficient mass of catalyst
comprising the catalyst (calculated based upon the content of
molecular sieve in the catalyst composite) is contained in the
isomerization zone to provide a weight hourly space velocity with
respect to the liquid feed stream (those components that are
normally liquid at STP) of from about 0.1 to 50 hr.sup.-1, and
preferably 0.5 to 25 hr.sup.-1.
[0055] The isomerization conditions may be such that the
isomerization is conducted in the liquid, vapor or at least
partially vaporous phase. For convenience in hydrogen distribution,
the isomerization is preferably conducted in at least partially in
the vapor phase. When conducted at least partially in the vaporous
phase, the partial pressure of C.sub.8 aromatics in the reaction
zone is preferably such that at least about 50 mass-% of the
C.sub.8 aromatics would be expected to be in the vapor phase. Often
the isomerization is conducted with essentially all the C.sub.8
aromatics being in the vapor phase.
[0056] The isomerization conditions are sufficient such that the
xylene isomer content approaches equilibrium. The conditions are
such that the isomerization product contains a xylene mixture is
which para-xylene comprises at least about 23 mass-%, ortho-xylene
at least about 21 mass-%, and meta-xylene at least about 48 mass-%
based upon total xylenes. Often, the feedstock is para-xylene
depleted, e.g., contains less than 5 mass-% para-xylene based upon
total xylene content, and the mass ratio of para-xylene to total
xylene in the product is at least about 0.235:1, and more
preferably, at least about 0.237:1. While the isomerization
conditions do not result in a xylene equilibrium being reached, the
close approach of the isomerization to equilibrium typically
results in an increase in the co-production of toluene and C.sub.9
and higher aromatics. The thinness of the outer layer and the
proximity of the hydrogenation metal component to the molecular
sieve are believed to contribute to the ability to have only a low
co-production of toluene and C.sub.9 and higher aromatics. That is,
the total toluene and trimethylbenzene make, based on the mass of
the C.sub.8 aromatics in the feedstock, is less than about 3,
preferably less than about 2.5, and most preferably less than about
2, mass-%. Preferably the isomerization conditions result in
little, if any, naphthenes being co-produced. Desirably the net
naphthene make (based upon total C.sub.8 aromatics in the
feedstock) is less than about 0.5, preferably less than about 0.2,
mass-%. Where very low net naphthene make is sought,
molybdenum-containing catalysts are favored. Often, the net
naphthene make using molybdenum catalysts can be less than about
0.05 mass-% based upon total C.sub.8 aromatics in the
feedstock.
[0057] In preferred catalysts, the binder comprises aluminum
phosphate which is believed to further reduce the co-production of
toluene and C.sub.9 and higher aromatics.
[0058] The particular scheme employed to recover an isomerized
product from the effluent of the reactors of the isomerization zone
is not deemed to be critical to the instant invention, and any
effective recovery scheme known in the art may be used. Typically,
the isomerization product is fractionated to remove light
by-products such as alkanes, naphthenes, benzene and toluene, and
heavy by-products to obtain a C.sub.8 isomer product. Heavy
by-products include dimethylethylbenzene and trimethylbenzene. In
some instances, certain product species such as ortho-xylene or
dimethylethylbenzene may be recovered from the isomerized product
by selective fractionation. The product from isomerization of
C.sub.8 aromatics usually is processed to selectively recover the
para-xylene isomer, optionally by crystallization. Selective
adsorption is preferred using crystalline aluminosilicates
according to U.S. Pat. No. 3,201,491. Improvements and alternatives
within the preferred adsorption recovery process are described in
U.S. Pat. No. 3,626,020, U.S. Pat. No. 3,696,107, U.S. Pat. No.
4,039,599, U.S. Pat. No. 4,184,943, U.S. Pat. No. 4,381,419 and
U.S. Pat. No. 4,402,832, incorporated herein by reference.
[0059] In the aspects of the processes of this invention where the
feedstock for isomerization has been previously subjected to
dealkylation conditions to reduce ethylbenzene content, the
feedstock often contains from about 0.5 to 10 mass-% ethylbenzene
based upon total C.sub.8 aromatics. Thus there is little advantage
in the layered catalyst exhibiting much activity toward
dealkylation. For many catalysts, steaming the catalyst can reduce
activity toward ethylbenzene dealkylation. Where dealkylation of
ethylbenzene is desired to be accomplished during xylene
isomerization, platinum group hydrogenation metal components are
usually preferred. Generally, where ethylbenzene dealkylation is
sought, the isomerization conditions are sufficient to convert at
least about 50, preferably at least about 60, mass-% of the
ethylbenzene in the feedstock.
[0060] Where the processes involve the isomerization of
ethylbenzene, usually the isomerization conditions are sufficient
that at least about 10, preferably between about 20 and 50, percent
of the ethylbenzene in the feed stream is converted. Generally, the
isomerization conditions do not result in a xylene equilibrium
being reached. Often, the mole ratio of xylenes in the product
stream is at least about 80, say, between about 85 and 95, percent
of equilibrium under the conditions of the isomerization. Where the
isomerization process is to generate para-xylene, e.g., from
meta-xylene, the feed stream contains less than 5 mass-%
para-xylene and the isomerization product comprises a para-xylene
to xylenes mole ratio of between about 0.20:1 to 0.25:1.
EXAMPLES
[0061] The following examples are presented only to illustrate
certain specific embodiments of the invention, and should not be
construed to limit the scope of the invention as set forth in the
claims. There are many possible other variations, as those of
ordinary skill in the art will recognize, within the spirit of the
invention.
Example I
[0062] Samples of catalyst are prepared.
[0063] Catalyst A: A molybdenum-impregnated aluminophosphate bound
MFI catalyst is prepared to represent the catalyst of the
invention. To a support material consisting of a 58 micron active
layer of 50 mass-% MFI zeolite (38 Si/AI.sub.2 ratio) and
aluminophosphate on an inert alpha alumina core (0.11 centimeter
diameter sphere) is added an aqueous solution of ammonium
heptamolybdate to give 0.73 grams of molybdenum per 100 grams of
MFI-aluminophosphate composition. After drying and calcination at
525.degree. C. for 2 hours in air with 3 mol-% steam, the catalyst
is reduced in hydrogen for 4 hours at 425.degree. C.
[0064] Catalyst B: A platinum-impregnated aluminophosphate bound
MFI catalyst is prepared. To a support material the same as used
for Catalyst A is added an aqueous solution of tetra-ammine
platinum chloride to give 0.034 grams of platinum per 100 grams of
MFI-aluminophosphate composition. After drying and calcination at
525.degree. C. for 2 hours in air with 3 mol-% steam, the catalyst
is reduced in hydrogen for 4 hours at 425.degree. C.
[0065] Catalyst C: A platinum-impregnated gamma alumina bound MFI
catalyst is prepared. A support material consisting of a 38 micron
active layer of 67 mass-% MFI zeolite (38 Si/AI.sub.2 ratio) and
gamma alumina binder on an inert alpha alumina core (0.11
centimeter diameter sphere) is treated with 10 mol-% steam in air
at 525.degree. C. for 3 hours. It is then contacted with an aqueous
solution of tetra-ammine platinum chloride to give 0.042 grams of
platinum per 100 grams of MFI-gamma alumina composition. After
drying and calcination at 525.degree. C. for 2 hours in air with 3
mol-% steam, the catalyst is reduced in hydrogen for 4 hours at
425.degree. C.
[0066] Catalyst D: A molybdenum-impregnated gamma alumina bound MFI
catalyst is prepared. To a support material consisting of a 60
micron active layer of 50 mass-% MFI zeolite (38 Si/AI.sub.2 ratio)
and gamma alumina binder on an inert alpha alumina core (0.11
centimeter diameter sphere) is added an aqueous solution of
ammonium heptamolybdate to give 0.91 grams of molybdenum per 100
grams of MFI-gamma alumina composition. After drying and
calcination at 525.degree. C. for 2 hours in air with 3 mol-%
steam, the catalyst is reduced in hydrogen for 4 hours at
425.degree. C.
[0067] Catalyst E is the same support as is used to make Catalysts
A and B.
[0068] Catalyst F is the support that is impregnated to make
Catalyst C.
Example II
[0069] Catalysts A to F are evaluated in a pilot plant for the
isomerization of a feed stream containing 15 mass-% ethylbenzene,
25 mass-% ortho-xylene and 60 mass-% meta-xylene. The pilot plant
runs are at a hydrogen to hydrocarbon ratio of 4:1. The pilot plant
runs are summarized in Table 1. The product data are taken at
approximately 50 hours of operation. The weight hourly space
velocities are based upon grams of zeolite loaded. TABLE-US-00001
TABLE 1 Cata- C D E F lyst A B Comp. Comp. Comp. Comp. WHSV, 15.9
15.9 43.6 31.8 31.5 43.6 hr.sup.-1 Inlet 400 370 382 378 372 392
360 Temper- ature, .degree. C. Pres- 689 689 689 689 689 689 689
sure, kPa g % Para- 23.9 23.9 23.8 23.7 23.9 23.2 23.5 xylene/
xylene EB Con- 75 50 75 75 75 50 50 version, % Toluene 1.5 0.8 1.9
4.3 4.4 1.4 3.0 and Trimethyl- benzene yield, mass-%
[0070] Example III
[0071] Catalyst G: To a support material consisting of a 200 micron
active layer of 10 mass-% MTW zeolite (39:1 Si/AI.sub.2 ratio) and
gamma alumina on a gamma alumina core (0.16 centimeter diameter) is
added an aqueous solution of chloroplatinic acid with 0.05 mass-%
hydrochloric acid to provide a final platinum level of 0.32 mass-%
on the catalyst. The impregnated pellets are then oxidized and
chloride adjusted at 565.degree. C. to yield 1.04 mass-% chloride
on the catalyst, subjected to a reducing environment of hydrogen at
565.degree. C., and sulfided with hydrogen sulfide to yield 0.09
mass-% sulfur on the catalyst. Scanning electron microscopy reveals
that over 90 mass-% of the platinum is contained in the outer
layer.
[0072] Catalyst H (comparative): To a support material consisting
of a 200 micron active layer of 10 mass-% MTW zeolite (39:1
Si/AI.sub.2 ratio) and gamma alumina on a gamma alumina core (0.16
centimeter diameter) is added an aqueous solution of chloroplatinic
acid with 2 mass-% hydrochloric acid to provide a final platinum
level of 0.31 mass-% on the catalyst. The impregnated pellets are
then oxidized and chloride adjusted at 565.degree. C. to yield 0.98
mass-% chloride on the catalyst, subjected to a reducing
environment of hydrogen at 565.degree. C., and sulfided with
hydrogen sulfide to yield 0.09 mass-% sulfur on the 5 catalyst.
Scanning electron microscopy reveals that less than 75 percent of
the platinum is contained in the outer layer.
Example IV
[0073] Catalysts G and H are evaluated in a pilot plant for
conversion of a feed stream containing 15 mass-% ethylbenzene, 25
mass-% ortho-xylene and 60 mass-% meta-xylene. The pilot plant runs
are at a hydrogen to hydrocarbon ratio of 4:1. The pilot plant runs
are summarized in Table 2. The product data are taken at
approximately 50 hours of operation. The weight hourly space
velocities are based upon grams of zeolite loaded. TABLE-US-00002
TABLE 2 Catalyst G H WHSV, hr.sup.-1 182 182 Inlet Temperature,
.degree. C. 382 382 Pressure, kPa g 689 689 % Para-xylene/xylene
22.9 22.5 EB conversion, % 35 31 Toluene and Trimethylbenzene
yield, mass-% 1.2 1.2
Example V
[0074] Catalyst I: A support material consisting of a 38 micron
active layer of 67 mass-% MFI zeolite (38:1 Si/AI.sub.2 ratio) and
gamma alumina binder on an inert alpha alumina core (0.11
centimeter diameter) is treated with 40 vol-% steam in air at
650.degree. C. for 6 hours. It is then contacted with an aqueous
solution of perrhenic acid to give 0.36 grams Re per 100 grams of
MFI-gamma alumina composition. After drying and calcination at
500.degree. C. for 2 hours in air, the catalyst is reduced in
hydrogen for 4 hours at 425.degree. C. and sulfided with hydrogen
sulfide to yield 0.03 mass-% sulfur on the catalyst.
[0075] Catalyst J: A support material consisting of a 60 micron
active layer of 50 mass-% MFI zeolite (38:1 Si/AI.sub.2 ratio) and
gamma alumina binder on an inert alpha alumina core (0.11
centimeter diameter) is treated with 90 vol-% steam in air at
750.degree. C. for 1.5 hours. It is then ion exchanged twice with
excess ammonium nitrate solution at 60.degree. C., washed, dried
and calcined in air at 550.degree. C. for 2 hours. It is then
contacted with an aqueous solution of perrhenic acid to give 0.45
grams Re per 100 grams of MFI-gamma alumina composition. After
drying and calcination at 500.degree. C. for 2 hours in air, the
catalyst is reduced in hydrogen for 4 hours at 425.degree. C. and
sulfided with hydrogen sulfide to yield 0.04 mass-% sulfur on the
catalyst.
Example VI
[0076] Calysts I and J are evaluated in a pilot plant for
conversion of a feed stream containing 15 mass-% ethylbenzene, 25
mass-% ortho-xylene and 60 mass-% meta-xylene. The pilot plant runs
are at a hydrogen to hydrocarbon ratio of 4:1. The pilot plant runs
are summarized in Table 3. The product data are taken at
approximately 50 hours of operation. The weight hourly space
velocities are based upon grams of zeolite loaded. TABLE-US-00003
TABLE 3 Catalyst I J WHSV, hr.sup.-1 16 16 Inlet Temperature,
.degree. C. 392 402 Pressure, kPa g 689 689 % Para-xylene/xylene
23.7 23.7 EB conversion, % 16 19 Toluene and Trimethylbenzene
yield, mass-% 0.3 0.6
Example VII
[0077] Catalyst K: Steamed and calcined aluminum-phosphate-bound
MFI zeolite spheres are prepared using the method of Example I in
U.S. Pat. No. 6,143,941. A catalyst is prepared by contacting the
support with chloroplatinic acid and 5 mass-% nitric acid to give
210 mass-ppm platinum on the finished catalyst. After drying and
calcining, the catalyst is reduced in hydrogen for 4 hours at
425.degree.C.
[0078] Catalyst L: A support material consisting of a 60 micron
active layer of 50 mass-% MFI zeolite (38:1 Si/AI.sub.2 ratio) and
gamma alumina binder on an inert alpha alumina core (0.11
centimeter diameter) is treated with 40 vol-% steam in air at
650.degree. C. for 6 hours. It is then contacted with an aqueous
solution of perrhenic acid to give 0.28 grams Re per 100 grams of
MFI-gamma alumina composition. After drying and calcination at
500.degree. C. for 2 hours in air, the catalyst is reduced in
hydrogen for 4 hours at 425.degree. C. and sulfided with hydrogen
sulfide to yield 0.04 mass-% sulfur on the catalyst.
[0079] Catalyst M: A reactor loading was prepared consisting of 24
mass parts Catalyst K at the reactor inlet followed by 76 mass
parts Catalyst L.
[0080] Catalysts K, L and M are evaluated in a pilot plant for
conversion of a feed stream containing 15 mass-% ethylbenzene, 25
mass-% ortho-xylene and 60 mass-% meta-xylene. The pilot plant runs
are at a hydrogen to hydrocarbon ratio of 4:1. The pilot plant runs
are summarized in Table 4. The product data are taken at
approximately 50 hours of operation. The weight hourly space
velocities are based upon grams of zeolite loaded. TABLE-US-00004
TABLE 4 Catalyst K L M WHSV, hr.sup.-1 10 22 6 Inlet Temperature,
.degree. C. 383 382 382 Pressure, kPa g 689 689 689 %
Para-xylene/xylene 20.4 21.6 23.9 EB conversion, % 79 7 78 Toluene
and Trimethylbenzene yield, mass-% 1.2 0.1 1.3
* * * * *